Biomechanics of Finger Pulleys during Climbing

  • Tan M
  • Fuss F
  • Niegl G
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Abstract

The A2-pulley was modelled as a structure consisting of 19 individual elastic pulleys with elastic inter-pulley connections. Each individual pulley results in 3 equations (force equilibria, and geometrical integrity) with 3 unknowns (pulley force, and co-ordinates of pulley-tendon contact). The 19 pulleys in sequence result into 57 2nd-order equations with 219 solutions, of which only one delivers all positive results. The model was used to determine the force distribution along the axial pulley length with respect to different tendon angles, in order to simulate different finger flexion angles in different climbing grip positions. Additionally, a pulley rupture and its propagation were simulated. It was shown that high finger flexion produces force spikes at the marginal fibres and should be avoided during climbing. This supports the conclusion that pulley injuries occur more during crimp grip than during open handgrip. Moreover, pulleys start to rupture at the marginal fibres. The rupture model, which is based on exclusion of fibres with forces higher than the failure force, shows that a pulley rupture is propagating instead of self-limiting. This seems logical when considering that the failure of one pulley fibre reduces the overall cross section of the pulley and thus increases the stress. Yet, once a pulley fibre has failed, the tendon angle decreases, in turn leading to a smaller fibre force. Considering both opposing factors, however, the loss of cross section is more significant than the reduction of the tendon angle, resulting in propagation of the rupture. Initially, the rupture rate is small and increases with time. This explains partial pulley ruptures, as a low initial rupture rate leaves some time for the pair reflex to unload the finger. Verf.-Referat

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Tan, M. A., Fuss, F. K., & Niegl, G. (2006). Biomechanics of Finger Pulleys during Climbing. In The Engineering of Sport 6 (pp. 241–246). Springer New York. https://doi.org/10.1007/978-0-387-46051-2_43

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